# MDX Essentials: Basic Set Functions: The CrossJoin() Function

This is the eighteenth article of the series, MDX Essentials. The series is designed to provide hands-on application of the fundamentals of the Multidimensional Expressions (MDX) language, with each tutorial progressively adding features designed to meet specific real-world needs.

For more information about the series in general, as well as the software and systems requirements needed for getting the most out of the lessons included, please see the first article, MDX at First Glance: Introduction to MDX Essentials.

Note: Service Pack 3 updates are assumed for MSSQL Server 2000, MSSQL Server 2000 Analysis Services, and the related Books Online and Samples.

### What We Accomplished in our Last Article

In the last article of the series, Basic Numeric Functions: The Count() Function, we took a break from purely set-related functions to focus on the numerical Count() function, as it is applied to sets. We introduced the Count() function, discussing its purpose, to return the number of cells in a specified set. We then exposed options within the syntax for overriding the default behavior of the function with regard to its handling of empty cells.

Along with an introduction to the purpose of the Count() function, we examined the syntaxes surrounding the function. We next undertook illustrative examples where we used Count(), both with and without the EXCLUDEEMPTY keyword, to meet a hypothetical business need. Finally, throughout the steps of our examples, we discussed the results we obtained using MDX.

As a part of the practice exercises in our last article, we performed a query using the CrossJoin() function. Our purpose was to use CrossJoin() as a “proofing” procedure, to ensure the accuracy and completeness of the results we obtained within our practice with the Count() function. As part of this exercise, we were afforded a preview of the CrossJoin() function, upon which we will focus this article.

### Introduction

In this lesson, we will expose another highly popular function in the MDX toolset, the CrossJoin() function. The general purpose of the CrossJoin() function is to allow us to produce all combinations of two sets. A primary driver for wanting to do this is to “collapse” two (or perhaps more) dimensions onto a single axis.

Uses of the CrossJoin() function can be quite sophisticated, and, as we shall learn, its use should be tempered with an understanding of its potential impact upon performance. We will introduce the function, commenting upon its operation and touching upon performance considerations at a general level, and then we will:

• Examine the syntax surrounding the function;
• Undertake illustrative examples of the uses of the function in practice exercises;
• Briefly discuss of the results datasets we obtain in the practice examples.
William Pearson
Bill has been working with computers since before becoming a "big eight" CPA, after which he carried his growing information systems knowledge into management accounting, internal auditing, and various capacities of controllership. Bill entered the world of databases and financial systems when he became a consultant for CODA-Financials, a U.K. - based software company that hired only CPA's as application consultants to implement and maintain its integrated financial database - one of the most conceptually powerful, even in his current assessment, to have emerged. At CODA Bill deployed financial databases and business intelligence systems for many global clients. Working with SQL Server, Oracle, Sybase and Informix, and focusing on MSSQL Server, Bill created Island Technologies Inc. in 1997, and has developed a large and diverse customer base over the years since. Bill's background as a CPA, Internal Auditor and Management Accountant enable him to provide value to clients as a liaison between Accounting / Finance and Information Services. Moreover, as a Certified Information Technology Professional (CITP) - a Certified Public Accountant recognized for his or her unique ability to provide business insight by leveraging knowledge of information relationships and supporting technologies - Bill offers his clients the CPA's perspective and ability to understand the complicated business implications and risks associated with technology. From this perspective, he helps them to effectively manage information while ensuring the data's reliability, security, accessibility and relevance. Bill has implemented enterprise business intelligence systems over the years for many Fortune 500 companies, focusing his practice (since the advent of MSSQL Server 2000) upon the integrated Microsoft business intelligence solution. He leverages his years of experience with other enterprise OLAP and reporting applications (Cognos, Business Objects, Crystal, and others) in regular conversions of these once-dominant applications to the Microsoft BI stack. Bill believes it is easier to teach technical skills to people with non-technical training than vice-versa, and he constantly seeks ways to graft new technology into the Accounting and Finance arenas. Bill was awarded Microsoft SQL Server MVP in 2009. Hobbies include advanced literature studies and occasional lectures, with recent concentration upon the works of William Faulkner, Henry James, Marcel Proust, James Joyce, Honoré de Balzac, and Charles Dickens. Other long-time interests have included the exploration of generative music sourced from database architecture.